1. Field of the Invention
The present invention relates to a motor controller for controlling a polyphase motor including a plurality of sets of windings and an electric power steering device using the motor controller.
2. Description of the Related Art
As a conventional electric power steering device, there is known an electric power steering device including, in a motor, two sets of windings, two inverters for controlling currents flowing through the respective winding sets, and individual power relays for supplying power from a power source to the respective inverters so that the current flowing through each of the winding sets is individually controllable (for example, see Japanese Patent Application Laid-open No. 2011-131860).
The conventional electric power steering device described in Japanese Patent Application Laid-open No. 2011-131860 cited above is configured as follows. In the case of a fault in one of the winding sets or the inverters, the power relay on the side where the fault has occurred is opened for the disconnection from the power source. The inverter on the normal side is controlled so that a torque is continuously output from the motor.
As described above, a motor controller for controlling a polyphase motor has a possibility of occurrence of the following faults as faults which may occur in the windings or the inverters of the motor. Specifically, the faults include abridging-type fault (also referred to as a short fault and an ON fault) such as abridging fault in a switching element, a ground fault in the winding of one of the phases, a ground fault in a wiring which connects the inverter and the winding, and a bridging fault between two phases, and an open-type fault such as disconnection of a wiring of any one of the windings or the inverters, and an open fault in any one of the switching elements included in the inverter.
In the case of the bridging-type fault or the open-type fault as described above, a torque pulsation occurs in a winding driving system in which the fault has occurred.
The conventional motor controller and the electric power steering device using the conventional motor controller do not distinguish the bridging-type fault and the open-type fault from each other in the case where the polyphase motor is controlled in the manner as described in Japanese Patent Application Laid-open No. 2011-131860 cited above. Therefore, in the case of some fault, there is a possibility that an overcurrent or a braking current generated by the bridging fault or the like flows. Therefore, power relays for stopping the faulty winding driving system are required to be provided so as to stop the supply of the currents from the power source to the inverter and the windings of the faulty winding driving system. In addition, a plurality of the power relays are required to be provided so as to correspond to the plurality of inverters. Thus, the number of components increases to make it difficult to downsize the motor controller and the electric power steering device. Further, a control system for turning ON/OFF the power relays is added. As a result, there is a problem in that a system becomes complex.